Residual Pressure, Checking
Fuel Pump, Checking
• When replacing the fuel delivery unit, check the fuel tank for visible contamination and clean if necessary.
Special tools, testers and auxiliary items required
• Pressure Tester (VAS 6550)
• Remote Control (V.A.G 1348/3A)
• Test Instrument Adapter/DSO (5-pin) (VAS 5565)
• Multi-meter (V.A.G 1715)
• Wrench (T10202)
• Measuring Container, 2 Liter
Residual Pressure, Checking
Conditions
• Fuel pressure OK and the (VAS 6550) is still connected. Checking fuel pressure, refer to => [ Fuel Pressure, Checking ]. Fuel Pressure, Checking
Sequence
- Activate the fuel pump with output Diagnostic Test Mode (DTM) to build fuel pressure.
- Check the fuel pressure on the (VAS 6550).
• Target value: 4.0 to 7.0 bar
- Watch the pressure decrease on the (VAS 6550). After 10 minutes the pressure must not drop below a 3.0 bar decrease.
If the pressure drops further:
- Activate the fuel pump with output DTM to build fuel pressure.
- Close the shut off valve - B - on the (VAS 6550) as soon as pressure accumulates. The level is perpendicular to the direction of flow.
If the Pressure No Longer Drops Now
• Check for the leak on the engine side. Repeat the residual pressure check. Close the shut off valve - A - this time to determine if there actually is a leak on the engine side.
- Check the fuel pipe to high pressure fuel pump for leaks.
If no malfunction can be found:
- Replace the high pressure fuel pump. Refer to => [ High Pressure Fuel Pump ] High Pressure Fuel Pump.
If the Pressure Drops Again
Check for the leak on the fuel tank side. Proceed as follows:
- Check the fuel line to the flange for leaks.
If no malfunctions are found on fuel line:
The pressure relief valve in the flange or pressure retention valve in the fuel pump leaks.
- Replace the flange with the fuel filter - item 20 -=> [ Flange with Fuel Filter ] Fuel Tank and Components Overview and repeat the pressure retention test. If the leak is still present, replace the fuel delivery unit.